The present invention generally relates to a method and device for transmitting data over a transmission medium at high speeds. More specifically, the present invention relates to using variations in electrical current for representing and conveying data over a transmission medium.
There are many modems on the market today for high speed data bit transmission on a twisted-pair of copper telephone lines. Constant demand for increased amounts of data bit transmission has generated the continual need for faster modems capable of transmitting and receiving greater amounts of data. While many high speed transmission techniques such as ADSL and HDSL have emerged in response to this technological demand, there continues to remain a demand for yet greater data transmission rates. In addition, it would be extremely advantageous if the technology incorporating the higher transmission rates were able to implement existing electrical communication infrastructure, i.e., twisted-pair telephone lines. An additional preference would allow for the transmission of these signals at lower power over greater distances without needing fewer or any repeaters to amplify the signal.
Conventionally, data transmission is sent via voltage signals that are susceptible to many factors that may adversely affect the quality and distance of the transmission. Some of these factors include: random distortion noise, inherent characteristics or poor physical condition of the transmission line, transmission line length, high frequency, attenuation and distortion effects. One common approach used to overcome some of these adverse affects is to increase the transmission power. Of course, the greater the distance, the greater the impedance and the likelihood of effects due to exposure to external noise sources. FCC regulations also limit frequency levels and power levels of transmission. Bridge taps and loading coils, present in phone line infrastructure also present significant impediments to voltage signal data transmission. Bridge taps tend to divide voltage signals hence weakening them. Loading coils tend to resist changes in voltage level hence degrading data characterized by voltage level.
The amount of data that can be transmitted is directly related to the number of quantization levels that a transmitter utilizes. Random distortion noise directly affects the amount of quantization levels. Attempting to increase a transmission rate by merely increasing the amount of quantization levels beyond that in which the data bits can be determined is not useful. To date, the limitations on quantization caused by random distortion noise has prevented conventional modems and transmission techniques from meeting the demand for higher data transmission speed.
Additionally, today""s transmission lines incorporate repeaters that amplify a signal that has attenuated or weakened during its transmission. The repeater is necessary to re-amplify the affected signal. A transmission signal that is expected to travel a great distance must often be re-amplified repeatedly.
Hence, prior to the present invention, a need existed for a method of data transmission capable of better recognizing and discriminating a signal from accompanying noise. Also needed, were methods and apparatus for transmitting data signals which would avoid or significantly reduce the adverse effects of the factors cited above, so as to provide data transmissions of higher quality, increased capacity, and longer transmission distances at lower power with fewer, or no need for repeaters.
This invention relates to data communication equipment (DCE), more specifically, a modem capable of high speed transmission of electronic data between data terminal equipment (DTE). Broadly stated, this invention sets forth a method and a device for transmitting data as a series of current pulses onto a transmission medium such as a communication line. The method requires converting an input signal waveform to a current signal waveform and transmitting the resulting current pulses onto a communication line wherein a predetermined bias voltage is maintained.
Transmitting data as current pulses is an improved method of transmitting data, as opposed to using voltage pulses, because current is not affected as much by capacitance. By virtue of Kirchoffs"" Law, this allows the transmission of data over greater distances because the signal is less attenuated by line capacitance. With an increase in shunt capacitance and/or an increase in frequency across the capacitance, voltage data pulses weaken. Therefore, bridge taps associated with the current phone line infrastructure will not degrade the signals transmitted according to the invention to the same degree as they degrade (divide) conventional voltage signal waveforms. It is also known that loading coils exist in the infrastructure, are resistant to voltage changes, hence, the loading coils present a significant impediment to voltage waveform signals. On the other hand, it is believed that signals transmitted according to the present invention should be far less affected by loading coils.
Another embodiment of this invention includes a method of generating representative pulses of current from an input (either current or voltage) waveform and transmitting resulting current pulses onto a communication line. Another aspect of the invention includes receiving the current pulses, measuring the current pulses, and translating the measured current pulses into data.
A circuit for carrying out the method as it relates to transmitting standard voltage-based data, includes a converter for receiving voltage waveform input and generating a series of current pulses in response to the input voltage signal. A transmitter responsive to output of the converter is provided for transmitting the output onto a communication line terminated by a receiver.
Another embodiment of the invention provides an automatic system for adjusting series and shunt impedance of a transmitting system relative to changes in data and transmission medium by a circuit for measuring and correcting changes in series and shunt impedance of the line using references internal to the transmitter (voltage, current, impedance, and current range). A gain amplifier is used to control changes in impedance and signal current. Output voltage is kept at a reference level while output current is varied thereby controlling the impedance of the transmitter. The transmitter has a current source for supplying reference currents and a voltage source for supplying reference voltages and a gain controlling circuit for controlling a current signal within a range of values according to binary input data.
A common problem of other known modems is the deterioration of the transmission signal due to distortion effects over the transmission line. In effect, the transmission signal is not able to be identified because of the accompanying noise distortion. This invention is able to transmit significantly greater amounts of data than previous methods because it discriminates transmitted data from random distortion noise existing on the communication line.
A primary advantage of this invention is the provision of significantly increased amounts of data by being able to transmit and receive a low voltage signal amidst the accompanying random distortion noise and interference that was generally thought to be indeterminable.
A further advantage of this invention is the provision of significantly increased lengths of transmission than currently thought capable without the use of repeaters or amplifiers.
Another aspect of this invention is to transmit data at a low voltage and to further maintain this low voltage by monitoring and adjusting the current associated with the data signal.
It is further contemplated that the transmitter step of monitoring and adjusting the current includes the step of transmitting at least one reference/calibration pulse over the communication line and measuring the effects of line impedance on the current pulse.
These and other features of the present invention are discussed or apparent in the following detailed description.